html {
  height: 100%;
  background: radial-gradient(ellipse at bottom, #1b2735 0%, #090a0f 100%);
  overflow: hidden;
}
.title {
  position: absolute;
  top: 50%;
  left: 0;
  right: 0;
  color: #fff;
  text-align: center;
  font-family: "lato", sans-serif;
  font-weight: 300;
  font-size: 50px;
  letter-spacing: 10px;
  margin-top: -60px;
  padding-left: 10px;
  background: linear-gradient(white, #38495a);
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
}

@function getShadows($n) {
  $shadows: "#{random(100)}vw #{random(100)}vh #fff";
  @for $i from 2 through $n {
    $shadows: "#{$shadows}, #{random(100)}vw #{random(100)}vh #fff";
  }
  // 去掉双引号
  @return unquote($shadows);
}

$duration: 1000s;
$count: 1000;
@for $i from 1 through 5 {
  $duration: floor($duration/2);
  $count: floor($count/2);
  .layer#{$i} {
    position: fixed;
    $size: #{$i}px;
    width: $size;
    height: $size;
    border-radius: 50%;
    background: lightblue;
    box-shadow: getShadows($count);
    animation: moveup $duration linear infinite;
    &::after {
      content: "";
      position: fixed;
      width: inherit;
      height: inherit;
      left: 0;
      top: 100vh;
      border-radius: inherit;
      box-shadow: inherit;
    }
  }
}

@keyframes moveup {
  to {
    transform: translateY(-100vh);
  }
}
